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Sökning: db:Swepub > Persson Anders > Tidskriftsartikel > McKenna P.

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1.
  • Batani, D., et al. (författare)
  • Effects of laser prepulses on laser-induced proton generation
  • 2010
  • Ingår i: New Journal Of Physics. - Iop Publishing. - 1367-2630. ; 12
  • Tidskriftsartikel (refereegranskat)abstract
    • Low-intensity laser prepulses (<10(13) W cm(-2), nanosecond duration) are a major issue in experiments on laser-induced generation of protons, often limiting the performances of proton sources produced by high-intensity lasers (approximate to 10(19) W cm(-2), picosecond or femtosecond duration). Depending on the intensity regime, several effects may be associated with the prepulse, some of which are discussed in this paper: (i) destruction of thin foil targets by the shock generated by the laser prepulse; (ii) creation of preplasma on the target front side affecting laser absorption; (iii) deformation of the target rear side; and (iv) whole displacement of thin foil targets affecting the focusing condition. In particular, we show that under oblique high-intensity irradiation and for low prepulse intensities, the proton beam is directed away from the target normal. Deviation is towards the laser forward direction, with an angle that increases with the level and duration of the ASE pedestal. Also, for a given laser pulse, the beam deviation increases with proton energy. The observations are discussed in terms of target normal sheath acceleration, in combination with a laser-controllable shock wave locally deforming the target surface.
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2.
  • Burza, Matthias, et al. (författare)
  • Hollow microspheres as targets for staged laser-driven proton acceleration
  • 2011
  • Ingår i: New Journal of Physics. - Institute of Physics Publishing (IOPP). - 1367-2630. ; 13, s. 013030
  • Tidskriftsartikel (refereegranskat)abstract
    • A coated hollow core microsphere is introduced as a novel targetin ultra-intense laser–matter interaction experiments. In particular, it facilitates staged laser-driven proton acceleration by combining conventional target normal sheath acceleration (TNSA), power recycling of hot laterally spreading electrons and staging in a very simple and cheap target geometry. During TNSA of protons from one area of the sphere surface, laterally spreading hot electrons form a charge wave. Due to the spherical geometry, this wave refocuses on the opposite side of the sphere, where an opening has been laser micromachined.This leads to a strong transient charge separation field being set up there, which can post-accelerate those TNSA protons passing through the hole at the right time. Experimentally, the feasibility of using such targets is demonstrated. A redistribution is encountered in the experimental proton energy spectra, as predicted by particle-in-cell simulations and attributed to transient fields set up by oscillating currents on the sphere surface.
3.
  • Lundh, Olle, et al. (författare)
  • Active steering of laser-accelerated ion beams
  • 2008
  • Ingår i: Applied Physics Letters. - American Institute of Physics. - 0003-6951. ; 92:1
  • Tidskriftsartikel (refereegranskat)abstract
    • A technique for optical control of the spatial distribution of laser-accelerated ion beams is presented. An ultra-short laser pulse, tightly focused to relativistic intensities on a thin foil target, drives a beam of MeV ions. An auxiliary, nanosecond laser pulse drives a shock and locally deforms the initially flat target prior to the main pulse interaction. By changing the properties of the shock-driving laser pulse, the normal direction of the ion emitting surface is locally manipulated and the emission direction is thereby controlled. In the future, this method could be used to achieve dynamic control of the ion beam divergence.
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4.
  • Lundh, Olle, et al. (författare)
  • Influence of shock waves on laser-driven proton acceleration
  • 2007
  • Ingår i: Physical Review E. - American Physical Society. - 1539-3755. ; 76:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The influence of shock waves, driven by amplified spontaneous emission (ASE), on laser-accelerated proton beams is investigated. A local deformation, produced by a cold shock wave launched by the ablation pressure of the ASE pedestal, can under oblique laser irradiation significantly direct the proton beam toward the laser axis. This can be understood in the frame of target normal sheath acceleration as proton emission from an area of the target where the local target normal is shifted toward the laser axis. Hydrodynamic simulations and experimental data show that there exists a window in laser and target parameter space where the target can be significantly deformed and yet facilitate efficient proton acceleration. The dependence of the magnitude of the deflection on target material, foil thickness, and ASE pedestal intensity and duration is experimentally investigated. The deflection angle is found to increase with increasing ASE intensity and duration and decrease with increasing target thickness. In a comparison between aluminum and copper target foils, aluminum is found to yield a larger proton beam deflection. An analytic model is successfully used to predict the proton emission direction.
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5.
  • McKenna, P, et al. (författare)
  • High-intensity laser-driven proton acceleration: influence of pulse contrast
  • 2006
  • Ingår i: Philosophical Transactions A: Physical Sciences and Engineering. - Royal Society. - 1364-503X. ; 364:1840, s. 711-723
  • Tidskriftsartikel (refereegranskat)abstract
    • Proton acceleration from the interaction of ultra-short laser pulses with thin foil targets at intensities greater than 10(18) W cm(-2) is discussed. An overview of the physical processes giving rise to the generation of protons with multi-MeV energies, in well defined beams with excellent spatial quality, is presented. Specifically, the discussion centres on the influence of laser pulse contrast on the spatial and energy distributions of accelerated proton beams. Results from an ongoing experimental investigation of proton acceleration using the 10 Hz multi-terawatt Ti : sapphire laser (35 fs, 35 TW) at the Lund Laser Centre are discussed. It is demonstrated that a window of amplified spontaneous emission (ASE) conditions exist, for which the direction of proton emission is sensitive to the ASE-pedestal preceding the peak of the laser pulse, and that by significantly improving the temporal contrast, using plasma mirrors, efficient proton acceleration is observed from target foils with thickness less than 50 nm.
6.
  • Neely, D., et al. (författare)
  • Enhanced proton beams from ultrathin targets driven by high contrast laser pulses
  • 2006
  • Ingår i: Applied Physics Letters. - American Institute of Physics. - 0003-6951. ; 89:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The generation of proton beams from ultrathin targets, down to 20 nm in thickness, driven with ultrahigh contrast laser pulses is explored. the conversion efficiency from laser energy into protons increases as the foil thickness is decreased, with good beam quality and high efficiencies of 1% being achieved, for protons with kinetic energy exceeding 0.9 MeV, for 100 nm thick aluminum foils at intensities of 10(19) W/cm(2) with 33 fs, 0.3 J pulses. To minimize amplified spontaneous emission (ASE) induced effects disrupting the acceleration mechanism, exceptional laser to ASE intensity contrasts of up to 1010 are achieved by introducing a plasma mirror to the high contrast 10 Hz multiterawatt laser at the Lund Laser Centre. It is shown that for a given laser energy on target, regimes of higher laser-to-proton energy conversion efficiency. can be accessed with increasing contrast. The increasing efficiency as the target thickness decreases is closely correlated to an increasing proton temperature. (c) 2006 American Institute of Physics.
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